President Trump threatens James Comey in tweet about "tapes"

(CNN) President Donald Trump issued a thinly veiled threat Friday to fired FBI Director James Comey, an extraordinary development in the ongoing feud between the President and the agencies investigating alleged ties between his campaign and Russia.

"James Comey better hope that there are no 'tapes' of our conversations before he starts leaking to the press," the President tweeted.

When he fired Comey earlier this week, Trump garnered comparisons to President Richard Nixon and his infamous decision to remove the special prosecutor investigating Watergate crimes in 1973. The Watergate scandal accelerated drastically when it was revealed Nixon taped conversations in the White House. Trump didn't provide further details Friday on whether he was taping conversations.

Soon after tweeting the threat to Comey, Trump invoked former Director of National Intelligence James Clapper, who testified before the Senate earlier this week that he was not aware of any evidence demonstrating collusion between Trump's campaign and Russia.

"When James Clapper himself, and virtually everyone else with knowledge of the witch hunt, says there is no collusion, when does it end?" Trump tweeted.

Clapper, however, qualified his remarks by saying he had been unaware of an FBI investigation into the matter until Comey announced it to the public at a House hearing in March. And it's unclear how much Clapper would know about developments in the investigation after he left office earlier this year.

It's not unheard of for presidents to record conversations, using different systems to do so, with and without participants' knowledge. Six presidents secretly recorded meetings and telephone conversations between 1940 and 1973, according to historian and CNN contributor Julian Zelizer.

Trump's reasoning behind firing Comey

On Thursday, Trump, discussing the firing of Comey, told NBC News that he was frustrated by the ongoing investigation and believed it was motivated by Democrats' fury at losing the election.

Trump told NBC's Lester Holt: "And in fact when I decided to just do it, I said to myself, I said 'you know, this Russia thing with Trump and Russia is a made-up story, it's an excuse by the Democrats for having lost an election that they should have won.'"

A source close to Comey told CNN's Jake Tapper Wednesday there are two reasons why Trump fired the FBI director.

1. Comey never provided the President with any assurance of personal loyalty.

2. The FBI's investigation into possible Trump team collusion with Russia in the 2016 election was accelerating.

Comey has not yet responded to the Senate intelligence committee's invitation to testify in closed session next week, Democratic and Republican spokespersons for the committee told CNN Friday.